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| author | Thomas Gleixner <tglx@linutronix.de> | 2022-09-15 13:11:19 +0200 |
|---|---|---|
| committer | Peter Zijlstra <peterz@infradead.org> | 2022-10-17 16:41:11 +0200 |
| commit | 80e4c1cd42fff110bfdae8fce7ac4f22465f9664 (patch) | |
| tree | 72eb9d2152e2c6af9f82d92c4508302b0d044fe8 /arch/x86/Kconfig | |
| parent | bea75b33895f7f87f0c40023e36a2d087e87ffa1 (diff) | |
| download | lwn-80e4c1cd42fff110bfdae8fce7ac4f22465f9664.tar.gz lwn-80e4c1cd42fff110bfdae8fce7ac4f22465f9664.zip | |
x86/retbleed: Add X86_FEATURE_CALL_DEPTH
Intel SKL CPUs fall back to other predictors when the RSB underflows. The
only microcode mitigation is IBRS which is insanely expensive. It comes
with performance drops of up to 30% depending on the workload.
A way less expensive, but nevertheless horrible mitigation is to track the
call depth in software and overeagerly fill the RSB when returns underflow
the software counter.
Provide a configuration symbol and a CPU misfeature bit.
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20220915111147.056176424@infradead.org
Diffstat (limited to 'arch/x86/Kconfig')
| -rw-r--r-- | arch/x86/Kconfig | 19 |
1 files changed, 19 insertions, 0 deletions
diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig index e368fc0daa4a..6ae7fa4b8eb7 100644 --- a/arch/x86/Kconfig +++ b/arch/x86/Kconfig @@ -2523,6 +2523,25 @@ config CPU_UNRET_ENTRY help Compile the kernel with support for the retbleed=unret mitigation. +config CALL_DEPTH_TRACKING + bool "Mitigate RSB underflow with call depth tracking" + depends on CPU_SUP_INTEL && HAVE_CALL_THUNKS + select HAVE_DYNAMIC_FTRACE_NO_PATCHABLE + select CALL_THUNKS + default y + help + Compile the kernel with call depth tracking to mitigate the Intel + SKL Return-Speculation-Buffer (RSB) underflow issue. The + mitigation is off by default and needs to be enabled on the + kernel command line via the retbleed=stuff option. For + non-affected systems the overhead of this option is marginal as + the call depth tracking is using run-time generated call thunks + in a compiler generated padding area and call patching. This + increases text size by ~5%. For non affected systems this space + is unused. On affected SKL systems this results in a significant + performance gain over the IBRS mitigation. + + config CPU_IBPB_ENTRY bool "Enable IBPB on kernel entry" depends on CPU_SUP_AMD && X86_64 |